Aside from very many small fixes and improvements to various pages (by more than 30 contributors!), the most notable changes in man-pages-3.80 are the following:

A new ioctl_fat(2) man page, written by Heinrich Schuchardt, documents the ioctl() operations that are implemented for FAT filesystems.

Over the years, as various flags were added to the madvise() system call, the madvise(2) man page had failed to keep up with various details, and existing information in the page did not apply to the new flags. The page has been substantially revised and reorganized for this release.

Several more (mainly Section 2) pages add a C library/kernel ABI differences subheading that marks text that describes differences between the behavior of the glibc wrapper function described in the page and the underlying raw system call.